Nutrient Resorption among Species and Stands: Initial Results
By: Craig See, MS 2013
We are in the initial stages of determining nitrogen and phosphorus resorption rates, or the withdrawal of nutrients within leaves prior to their senescence, among the species of interest in our stands. This is being accomplished by comparing the nutrient content of green leaves harvested during the growing season to that collected from fallen leaves.
Fresh foliar samples were collected from sun leaves of five trees of the three dominant species in each plot using a pole pruner or 12 gauge shotgun, depending on canopy height. Litter was collected using net hammocks.
Freshly fallen leaves (leaf litter) were also collected using 3 net hamocks per plot, 12 per stand, following rain-free periods; collections were sorted by species in the field. Tissue samples were dried, weighed, and ground with a Wiley Mill to pass a 40 mesh screen. Sampled tissues were ashed in a muffle furnace, digested, and analyzed for phosphorus using ICP-OES at the SUNY-ESF facility. Nitrogen values from C:N ratios were found using a Vario EL C:N Analyzer at Cornell University.
For American beech, the percent N resorbed decreases relative to P with increasing stand age (Figure 4). A significant decrease is seen between white birch in young (C1, C2) and mid C4, C6, HB-mid, JB-mid) aged stands (Figure 5). Both findings suggest greater P limitation in older stands, which is consistent with recent MEL model predictions.